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JOURNAL AND PROCEEDINGS
OF THE
ROYAL SOCIETY
O F
NEW SOUTH WALES
Volume 137 Parts 3 and 4
(Nos 413–414)
2004
ISSN 0035-9173
Published by the Society
Building H47 University of Sydney
NSW 2006 Australia
Issued December 2004
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THE ROYAL SOCIETY OF NEW SOUTH WALES
OFFICE BEARERS FOR 2003-2004
Patrons His Excellency, Major General Michael Jeffery, AC, CVO, MC,
Governor General of the Commonwealth of Australia.
Her Excellency Professor Marie Bashir, AC, Governor of New South
Wales.
President Ms K. Kelly, BA (Hons) Syd
Vice Presidents Mr D.A. Craddock, BSc(Eng) NSW, Grad.Cert. Management UWS.
Prof. W.E. Smith, MSc Syd., MSc Oxon, PhD NSW, MInstP, MAIP.
Mr C.F. Wilmot
Mr J.R. Hardie, BSc Syd., FGS, MACE.
one vacancy
Hon. Secretary (Gen.) Prof. J.C. Kelly, BSc Syd., PhD Reading, DSc NSW
Hon. Secretary (Ed.) Prof. P.A. Williams, BA (Hons), PhD Macq.
Hon. Treasurer Dr R.A. Creelman, BA, MSc, PhD
Hon. Librarian Ms C. Van Der Leeuw
Councillors Dr Eveline Baker
Dr Anna Binnie, PhD
Dr M.D. Hall
Dr M.R. Lake, Ph.D Syd
A/Prof. W. Sewell, MB, BS, BSc Syd., PhD Melb., FRCPA
Mr M.F. Wilmot, BSc
Mr R. Woollett
Ms M. Haire
Ms J. Rowling BEng UTS
Ms R. Stutchbury
Southern Highlands Rep. Mr H.R. Perry, BSc.
The Society originated in the year 1821 as the Philosophical Society of Australasia. Its main function is
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ISSN 0035-9173
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Journal & Proceedings of the Royal Society of New South Wales, Vol. 137, p. 99–122, 2004
ISSN 0035-9173/04/020099–24 $4.00/1
Gemstone Characteristics,
North-East Barrington Plateau, NSW
d.l. roberts† , f.l. sutherland‡⋆ , j.d. hollis†⋆ , p. kennewell† and i.t. graham⋆ .
Abstract: Corundum and zircon concentrates from gravel deposits in two northern Barring-
ton plateau prospects were studied for their features, to investigate potential gemstone sources
within the catchment zone. The studies utilized field research, colour sorting, gemmological
microscopy, EDAX and PIXE trace element analysis and zircon fission-track dating. The re-
sults showed statistical differences in corundum suites from different gravel horizons, which
suggested different source areas. Anorthoclase and ilmenorutile were identified as inclusions
in Barrington corundums for the first time. Zircon fission-track results showed that several
episodes of volcanic eruptions were involved (66–4 Ma), reinforcing and adding to previous
eruption ages. This suggests multiple corundum delivery both in space and time into drainage
systems.
Keywords: Corundum, ruby, gravels, terraces, eruption, trace elements, mineral inclusions,
zircon, gemstone sources.
INTRODUCTION 2. Detailed fission-track dating on zircons
concentrated from the northeastern Barrington
The Barrington volcanic plateau, 150 km north- field that helps to clarify the extent of gem bear-
northwest of Newcastle (Figure 1, page 117) ing eruptive episodes in this area.
is one of the many basalt lava fields in east-
ern Australia (Mason 1989, O’Reilly and Zhang GEOLOGICAL SETTING
1995, Sutherland and Fanning 2001). The field
is particularly noted for its association with The general geology of the Barrington Plateau
gemstones (ruby, sapphire, zircon), brought up region, its economic deposits and literature are
in multiple basaltic eruptions between 60 and outlined in Gilligan et al. (1987) and Suther-
4 Ma and concentrated by erosion into adja- land and Graham (2003). The general geology
cent alluvial deposits (Sutherland et al. 1998, of the study area in the North-East Barrington
Sutherland and Fanning 2001). The presence Plateau is summarised below.
of gem quality ruby in the Barrington deposits Basement geology consists of Late Devonian
(Webb 1997) has promoted investigations into to Early Carboniferous mudstone and siltstone
the economic potential of the gem deposits by with minor interbedded conglomerate, lithic
the Australian exploration and mining company sandstone and limestone. Most of this mate-
Cluff Resources Pacific NL. Exploration and rial was deposited in a deep marine environ-
testing programs have been concentrated in the ment. The sheet-like deposits of greywacke
northeastern part of the province, particularly within the mudstone were probably deposited
in the terraces and recent alluvial deposits of the by turbidity currents, while some of the con-
upper Manning River at Gummi Flats. Plates 1 glomerates may have been deposited as sub-
to 3 show examples of rubies and sapphire from marine fans. A Permian hornblende-biotite
the Gummi Flats deposits. granodiorite pluton and associated dykes in-
This study presents: truded through the folded Devonian, Carbonif-
1. The first detailed comparison of corun- erous and Early Permian sedimentary rocks at
dums found in the Gummi Flats terraces, to as- Gummi Flats. These sequences are capped
sist in evaluating their origin and distance trav- mostly by Cenozoic basaltic flows.
elled from source regions. This volcanic activity most likely extended
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100 ROBERTS et al.
from around 60 Ma to perhaps < 5 Ma. Alkali This grey gravel horizon ranges in thickness
basaltic flows and tuffaceous and fragmented up to 0.5 m and overlies the lower gravel hori-
volcanics are common, and form the resistant zon for approximately 55 m strike-length in the
plateau region. Underlying these massive basalt test trench. It is moderately to well sorted
flows is a basaltic horizon containing highly and exhibits mostly rounded to sub-rounded
altered basalt bombs. The sequence includes lithic fragments with sizes from sub-mm up to
ankaramitic basalt that may mark an intrusive 250 mm. There is an upward fining in the se-
sheet. quence, and a grey clay matrix makes up ap-
This elevated basalt plateau has been sub- proximately 45% volume of this horizon. Lithic
jected to radial drainage patterns over time, types include, igneous, metamorphic and meta-
cutting into the basalts and underlying Palaeo- sedimentary rocks. Generally more granodior-
zoic sediments and granodiorites. Local stream ite fragments are present than in the underlying
and drainage patterns have accumulated clasts gravel horizon.
of these rocks as well as gem stones in many (B). Lower gravel horizon of the Upper Terrace
river flats and catchment areas. Changes in (Section 18-B; Figure 3).
stream patterns and velocities have created This gravel contains rounded to sub-angular,
river terraces in localised areas. igneous, metamorphic and meta-sedimentary
lithic fragments, with sizes ranging from sub-
mm to > 256 mm. The horizon is up to 2.6 m
STUDY AREA thick and has a reddish fine sandy clay matrix,
Two study sites were investigated in this study with occasional sand and silt lenses up to 20 cm
in the northern Barrington Plateau. in length and 10 cm thick. There is indistinct
upward fining, but generally the horizon is very
poorly sorted. This horizon is overlain in part
Gummi Flats Area
by the grey gravel horizon (Section 18-A), and
The main sampling sites for corundum and zir- a medium grey sand or a fine silty clay. Hu-
con included sections of older terraces and the mus topsoil some 0.5 m thick caps the sequence.
present alluvial terrace deposits of the upper Weathered granodiorite forms the underlying
Manning River. These lie below the eastern basement.
edge of the basalt field both upstream and (C). Middle Terrace horizon
downstream of Backwater Creek junction (Fig- (Section T4A; Figure 4, page 103).
ure 2, page 101). The deposits were excavated The horizon consists of sub-rounded to sub-
during bulk testing and sampling programs by angular, igneous, metamorphic and meta-
Cluff Resources Pacific NL, during the period sedimentary rocks. Rock sizes vary from sub-
2000–2003. mm to > 256 mm. An orange clay matrix,
Suites of corundums were recovered from with sporadic black clay lenses up to 20 cm
heavy mineral concentrates from four specific thick underlies a grey gravel in some places.
gravel horizons: The upper (A) and lower (B) Some fragments show heavy manganese stain-
horizons of the Upper Terrace deposit (Trench ing. The horizon ranges up to 2.5 m thick, is
11); the Middle Terrace deposit (C; Trench 4A) poorly sorted but shows a slight fining upwards.
and Recent alluvial deposit (D; Trench 2A). Basement is weathered granodiorite, and large
The zircons were recovered from heavy mineral sporadic fresh granodiorite boulders appear at
concentrates from the Upper Terrace deposit the base of the gravels. A fine sandy clay of
(Trench 11). varying colour overlies the gravel horizon, and
(A). Upper gravel horizon of the Upper Terrace is up to 2.7 m thick. Black organic topsoil cover
(Section 18-A; Figure 3, page 102). is variable, but averages 0.5 m.
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GEMSTONE CHARACTERISTICS 101
Figure 2. Sample site locations, Gummi Flats, Manning River deposits, with schematic section
showing gem-bearing deposits (inset).
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102 ROBERTS et al.
(D). Recent Alluvials
(Section T2A; Figure 5, page 103).
The gravel horizon here is composed of igneous,
metamorphic and meta-sedimentary rocks, that
are sub-angular to sub-rounded, with a colour
gradation laterally from grey, black, grey-brown
to light brown. Rocks range from sub-mm to
> 256 mm, with most exhibiting sub-rounded
to rounded shape. The horizon is up to 2.6 m
thick. A sandy clay and clay overlies the hori-
zon below a black humus topsoil. The basement
is weathered granodiorite.
East Tomalla
East Tomalla is an alluvial site, within the
basalt field itself (Figure 1, page 117). This
site produced zircons from a ruby prospect, and
is 3 km northwest of the Gummi Flats deposits
(G. Jeffreys lease). The site at 1160 m asl lies
at the head of a small tributary creek that
drains a local basalt cap that rises to 1200 m
asl. The drainage descends north into Toma-
lla Creek and the alluvial deposit consists of an
upper 30 cm of coarse gravels with heavy miner-
als concentrated towards the base and overlies a
0.5 m layer of clay. The overlying basalt shows
cracking and pitting which is typical of the
weathering of nepheline-bearing lavas. It con-
tains prominent megacrysts of spinel and sparse
clinopyroxene (up to 5 cm), sporadic xenoliths
of spinel-metaperidotite (up to 8 cm) and rare
granulites (up to 6 cm). This basanite flow
descends north to 1075 m asl, where it over-
lies ‘deep lead’ alluvial deposits. These con-
tain fragments of metasediments, igneous rocks
and waterworn boulders of silicified conglomer-
ate up to a meter across from basement sources.
Obvious fragments of typical Barrington basalts
are not seen. Heavy mineral concentrates from
the East Tomalla zircon site for fractions both
above and below 2 mm size range are described
in Appendix 1.
Figure 3. Cross-section, showing Section 18-A
and 18-B in the Upper Terrace.
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GEMSTONE CHARACTERISTICS
Figure 4. Cross-section, showing Section T4A in the Middle Terrace.
Figure 5. Cross-section, showing Section T2A in the Recent Alluvials.
103
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104 ROBERTS et al.
METHODOLOGY dum features. (Figures 6 and 7, pages 118 to
120).
Corundum Suites Previous work on Gummi alluvial corun-
dums (Sutherland and Coenraads 1996; Suther-
Representative suites of corundums were sam- land et al. 1998) demonstrated that the Pink
pled from each of the corundum concentrates - Red Group and some Blue Group corundums
obtained from the four study horizons. The have mineral inclusions such as sapphirine, trace
number of corundums studied from each suite element ratios with Cr / Ga > 1 and colour
was considered to represent statistical sets, absorption patterns (decreasing absorption at
based on earlier work using check monitoring 600–850 nm) that typify metamorphic origins.
of more extensive counting from one of the Some Blue, Green, Yellow and related Grey -
corundum suites. The statistical method used Brown - Black corundums however, have dif-
for this study, involved ‘carat weight (ct) / ferent mineral inclusions (e.g. peonaste spinel),
sample %’ analysis of corundums. The fol- trace element ratios with Cr / Ga < 1 and colour
lowing sample weight to percentage ratios are absorption (sustained or increasing absorption
as follows. 0–5 ct(100%), 6–10 ct(50%), 11– between 600–850 nm) that characterise mag-
20 ct(30%), 21–30 ct(20%), 31–40 ct(10%), 41– matic origins.
60 ct(7%), 61–100 ct(5%). Note that when in- To supplement this work, further trace el-
dividual suites exceeded 100 ct, the percentage ement determinations were made on Gummi
of stones analysed was calculated to conform to corundums by Proton-induced X-Ray Emmis-
the above mentioned ct/% calculations, e.g. if sion (PIXE) methods and are presented in Table
sample weight was 200 ct then 3% of the sample 3. The analyses were made on the PIXE analyt-
would be analysed. ical facility at Guelph University, Canada, using
The selected corundums were viewed un- a beam current between 1 to 3 nA, a charge ac-
der a gemmological binocular microscope and cumulation above 0.5 µc and approximately 5
the visible features noted, among a range of minutes analytical time per sample (M.I. Gar-
physical parameters. These parameters in- land, University of Toronto, analyst). A my-
cluded: colour, magmatic corrosion (resorp- lar filter was used to eliminate the intense Al
tion), alluvial abrasion, fusion crusts, fracture X-rays produced by the corundum, which elim-
surfaces, percussion marks, mineral inclusions, inated some light element determinations (e.g.
hydrothermal fluid lines and growth zoning. Mg).
The mineralogy of surface crusts and exposed The overlap in characteristics for the Blue
inclusions in the corundums were investigated Group Gummi corundums makes precise assign-
using an EDAX system, linked to a JEOL JXA- ment of the origin of these stones uncertain in
8600 Superprobe, in the School of Science, Food this colour group (Tables 1 and 2 on pages 106,
and Horticulture, BRCI campus, North Parra- 107; Figures 6 and 7). However specific fea-
matta, University of Western Sydney. tures, such as colour growth zoning, may indi-
The examined corundums were divided into cate a magmatic origin, while specific inclusions
five separate colour groups and percentages of such as sapphirine may indicate a metamorphic
each feature noted within them are listed in Ta- origin.
ble 1, (Upper Terrace - upper and lower hori-
zons) and Table 2, (Middle Terrace and Recent Zircon Suites
Alluvials). Colour ranges were further subdi-
vided for each unit/suite into a Colour-Shade Zircon grains up to 2 mm in size from each of
grouping, (e.g. very pale, pale, medium and the two study sites were grouped into colour
dark). The percentages of features counted in subsets prior to submission to Geotrack Inter-
each colour subdivision are presented as a se- national P.L., for mounting, etching and ir-
ries of histograms and represent a more detailed radiation at the Lucas Heights NSW reactor.
analysis of colour sorting and associated corun- The resultant fission-track counting used a Zeiss
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GEMSTONE CHARACTERISTICS 105
AXIOplan microscope. Details of the analyt- while a further 10.7% show resorption, and only
ical methods and statistical treatments used in < 2% of stones show percussion marks.
the analyses are outlined in Green (1981, 1983), Yellowish Group (BGY) Nearly 86% exist
Galbraith (1981, 1988, 1990) and Hurford and as resorbed and fractured stones. Stones show-
Green (1982, 1983). The fission-track results ing only resorption make up 14.2%. Nearly 5%
are summarised in Tables 4 and 5 on page 111. contain spinel inclusions.
Greenish Group (BGY) Nearly 95% show
RESULTS resorption and heavy fracturing, 5.4% show only
heavy fracturing, whilst 5.2% show a combina-
EDAX Analysis tion of resorption and heavy fracturing, along
with spinel inclusions.
Analysis identified the following mineral phases Blue Group (BGY) Nearly 99% show both
associated with the corundums in inclusions resorption and heavy fracturing, with 2.4% con-
and alteration crusts. Mineral inclusions iden- taining spinel inclusions and 1.2% showing per-
tified were Mg-rich to Fe-rich pleonaste to her- cussion marks. Some 1.5% of stones show only
cynite spinel, sapphirine, anorthoclase feldspar, fracturing.
ilmenorutile and a magnesium-iron aluminosil-
icate. The spinels and sapphirine were pre- Section 18-A, upper gravel horizon (Upper
viously recorded from Barrington Tops corun- Terrace)
dums, but anorthoclase and ilmenorutile are
Ruby Group Here 52.6% show a combination
new records as inclusions in these corundums.
of resorption and heavy fracturing, 1.9% show
Differences in fusion crust mineralogy were also
a fusion crust and 0.5% have percussion marks.
noted, with Mg and Fe-rich spinels being the
Some 3.5% of stones contain spinel, sapphirine
most common, although aluminosilicates (mul-
or ilmenite (optical identification) as inclusions.
lite) were also present. Some specimens exhib-
ited fusion crusts combining both Mg-rich and Grey-Brown-Black Group (GBB) Only
Fe-rich spinel, but usually on different sides of 7.4% of stones show either resorption or heavy
the stone. fracturing, 2.8% contain spinel inclusions, while
0.3% have a fusion crust and 0.3% show percus-
Grouped Corundum Features sion marks.
Yellowish Group (BGY) While 19.7% of
The main aspects of the features found in dif- stones show only resorption, nearly 78% of
ferent corundum groups (Tables 1 and 2) are stones show a combination of resorption and
summarized for each sample horizon. Three heavy fracturing. About 4% have spinel inclu-
main corundum groups are considered, a sions, 1.3% show percussion marks and 2.6% of
Ruby Group, with colours ranging from dark stones show only heavy fracturing of which 1.3%
red to very pale pink, a Grey-Brown-Black have a fusion crust.
Group (GBB), and a Blue-Green-Yellow Group Greenish Group (BGY) About 77% show
(BGY). resorption and heavy fracturing, 3.8% con-
Section 18-B, lower gravel horizon (Upper Ter- tain spinel inclusions and 1.9% show percussion
race) marks. About 23% show resorption as the only
feature.
Ruby Group Over 80% of these corundums ex-
Blue Group (BGY) Nearly 74% have a com-
hibit both magmatic resorption and heavy frac-
bination of resorption and heavy fracturing and
turing, while another 14% show either resorp-
of these 0.5% are fusion crusted stones. Some
tion or heavy fracturing. Nearly 2% have a sur-
3.2% have percussion marks and 2% of these
face fusion crust, 3.3% include percussion marks
show heavy fracturing only. Another 24.8% of
and 0.4% contain sapphirine inclusions.
stones are resorbed, with only 0.6% having per-
Grey-Brown-Black Group (GBB) Nearly
cussion marks.
85% combine resorption and heavy fracturing,
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106
‘Yellowish’ (BGY)
‘Yellowish’ (BGY)
‘Greenish’ (BGY)
‘Greenish’ (BGY)
‘Blue’ (BGY)
‘Blue’ (BGY)
Metamorphic
Metamorphic
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Magmatic
Magmatic
Magmatic
Magmatic
Magmatic
Magmatic
(GBB)
(GBB)
‘Ruby’
‘Ruby’
R 37.4 6.7 19.7 23.0 24.4 R 10.7 10.2 14.2 5.2 22.8
F 6.4 0.7 1.3 2.0 F 3.6 2.2 5.4 1.5
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R-F 50.3 89.2 72.5 71.3 67.8 R-F 80.1 83.0 81.1 84.2 72.1
R-C 0.7 R-C
F-C 1.3 F-C
R-SpI 0.8 0.5 R-SpI 2.6
F-SpI 0.5 F-SpI
R-SapI 0.5 R-SapI
ROBERTS et al.
F-SapI 1.6 F-SapI
R-P 0.6 R-P
F-P F-P
R-F-C 1.2 0.3 0.5 R-F-C 1.9
R-F-SpI 0.4 1.8 3.9 3.8 1.7 R-F-SpI 2.8 4.7 2.6 2.4
R-F-SapI 0.1 R-F-SapI 0.4
R-F-ILI 0.1 R-F-ILI
R-F-P 0.5 0.3 1.3 1.9 3.2 R-F-P 3.3 1.8 1.2
R-C-SpI R-C-SpI
R-C-SapI R-C-SapI
F-SpI-P F-SpI-P
R-F-C-SpI R-F-C-SpI
R-F-C-SapI R-F-C-SapI
ZONED 11.1% ZONED 2.6%
No. of stones No. of stones
analysed: 116 117 21 38 65 analysed: 276 204 76 52 114
Section 18-A Section 18-B
Upper Terrace, Upper Horizon Gravels Upper Terrace, Lower Horizon Gravels
Grouped percentages Grouped percentages
Table 1. Grouped corundum percentages, from the Upper Terrace, Sections 18-A and 18-B. R Shows Resorption, F Heavily Fractured,
C Fusion Crust, P Percussion Marks, SpI Spinel Inclusions, SapI Sapphirine Inclusions, Ili Ilmenite Inclusions
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‘Yellowish’ (BGY)
‘Yellowish’ (BGY)
‘Greenish’ (BGY)
‘Greenish’ (BGY)
‘Blue’ (BGY)
‘Blue’ (BGY)
Metamorphic
Metamorphic
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Corundum
Magmatic
Magmatic
Magmatic
Magmatic
Magmatic
Magmatic
(GBB)
(GBB)
‘Ruby’
‘Ruby’
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R 7.8 7.1 30.8 7.7 12.2 R 14.4 23.1 10.0 23.6
F 8.7 1.8 15.5 F 1.9
R-F 71.7 84.8 69.2 69.2 84.7 R-F 28.1 69.4 60.0 78.6 64.5
R-C R-C 12.2
GEMSTONE CHARACTERISTICS
F-C F-C
R-SpI 0.4 R-SpI
F-SpI 0.8 7.6 F-SpI 10.0
R-SapI R-SapI
F-SapI F-SapI
R-P R-P 2.5 10.0
F-P F-P
R-F-C 2.3 1.6 R-F-C 28.1 7.2 2.3
R-F-SpI 3.1 1.6 R-F-SpI 2.5 10.0 14.2 4.0
R-F-SapI 1.2 R-F-SapI 5.1
R-F-ILI R-F-ILI
R-F-P 1.7 2.3 3.1 R-F-P 3.5 1.8
R-C-SpI 0.9 R-C-SpI 2.5
R-C-SapI 0.7 R-C-SapI
F-SpI-P F-SpI-P 1.9
R-F-C-SpI 0.8 R-F-C-SpI 3.1 2.5
R-F-C-SapI 0.7 R-F-C-SapI 3.0
ZONED 13.5% ZONED
No. of stones No. of stones
analyzed: 105 105 13 13 76 analyzed: 53 43 10 14 58
Section T2A, Recent Alluvials, Grouped percentages Section T4-A, Middle Terrace, Grouped percentages
Table 2. Grouped corundum percentages, from the Middle Terrace (Section T4A) and the Recent Alluvials (Section T2A). R Shows Resorption,
F Heavily Fractured, C Fusion Crust, P Percussion Marks, SpI Spinel Inclusions, SapI Sapphirine Inclusions, Ili Ilmenite Inclusions
107
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108 ROBERTS et al.
Section T4A (Middle Terrace) Yellowish Group (BGY) Around 69% of
stones are resorbed and heavily fractured, with
Ruby Group Almost 71% of stones show re- 30.8% showing resorption only.
sorption and heavy fracturing, 34.2% contain
Greenish Group (BGY) In this group 92.4%
fusion crusts, while 8.1% contain sapphirine in-
are resorbed or heavily fractured or a combina-
clusions, 3.1% spinel inclusions and 3.5% show
tion of both, while 7.6% are heavily fractured
percussion marks. Some 14.4% show only re-
and contain spinel inclusions.
sorption and 12.2% show resorption with fusion
crusts. Blue Group (BGY) Nearly 85% show resorp-
tion and heavy fracturing, while 3.1% are re-
Grey-Black-Brown Group (GBB) Nearly sorbed, heavily fractured with percussion marks
75% of stones are resorbed and heavily frac- and 12.2% show resorption only. Some 13.5% of
tured, with 5% containing spinel inclusions and the group show growth zoning.
2.5% a fusion crust. Otherwise 23.1% are re-
sorbed only and 2.5% are resorbed and show
percussion marks.
Colour-Shade Features
Yellowish Group (BGY) Only 70% of stones
are resorbed and heavily fractured with 10% The main features in each colour shade group
of these containing spinel inclusions. Just 20% (Figures 6 and 7) are summarised for each
show resorption with 10% of these having per- shade.
cussion marks. Stones showing only heavy frac-
turing but containing spinel inclusions account Ruby Group
for 10% of the suite.
Very Pale The Middle Terrace (T4A) lacks
Greenish Group (BGY) All stones show re-
very pale pinks. The other 3 terraces feature
sorption and heavy fracturing, with 7.2% of
strong percentages of heavily fractured and re-
these having a surface fusion crust and 14.2%
sorbed stones. The Upper Terrace (Section 18-
spinel inclusions.
B), contains some small percentages (< 2%)
Blue Group (BGY) About 73% show resorp- with sapphirine mineral inclusions.
tion and heavy fracturing, with 2.3% having a Pale Resorption and heavy fracturing dominate
fusion crust. Some 4% contain spinel inclusions as features throughout all four sections. The
and 1.8% show percussion marks, Just 23.6% of Recent Alluvials (Section T2A) and Middle Ter-
this suites stones show resorption only, nearly race (Section T4A) show the most variation be-
2% show heavy fracturing only and just 1.9% tween features and mineral inclusions.
show heavy fracturing, percussion marks and
spinel inclusions. Medium Section 18-B (Upper Terrace) shows
stones with spinel inclusions and fusion crusts in
Section T2A, Recent Alluvials < 10% of the suite. Middle terrace (T4A) grav-
els show up to 38% stones with fusion crusts and
Ruby Group Nearly 82% of stones are re- 9.5% spinel inclusions. Recent Alluvials (T2A)
sorbed and heavily fractured showing combina- stones have spinel, sapphirine inclusions, plus
tions of either spinel or sapphirine inclusions, fusion crusts in amounts < 5%.
fusion crusts and percussion marks. Only 9.8% Dark Resorbed and heavily fractured stones
show resorption as the main feature. feature heavily in the upper terrace horizons.
Grey-Brown-Black Group (GBB) Some The Recent Alluvials (T2A) and Upper Terrace
90.3% are resorbed and heavily fractured, while gravel horizons contain stones with spinel and
3.2% contain spinel inclusions and fusion crusts sapphirine inclusions plus fusion crusting in <
and 2.3% show percussion marks. Only 1.8% 10%. Middle Terrace gravels contain no stones
are just fractured and 0.8% are fractured with with mineral inclusions. However fusion crust-
spinel inclusions. ing is present in around 35% of the suite.
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GEMSTONE CHARACTERISTICS 109
Grey-black-brown Group (GBB) zons. The Middle Terrace (T4A) shows approxi-
mately 10% assemblages of spinel inclusions and
Very Pale Resorption and heavy fracturing
resorbed or heavily fractured stones with per-
dominate. Less than 10% of stones show spinel
cussion marks.
inclusions in both horizons of the Upper Ter-
Greenish Resorbed and heavily fractured
race, plus approximately 2% show fusion crust
stones are dominant features in all suites. Only
and percussion marks.
the Middle Terrace has stones with > 10%
Pale Over 80% of stones in the Upper Ter-
spinel inclusions.
race horizons and Recent Alluvials (T2A) fea-
ture resorption and heavy fracturing, and < Apricot Group
5% with spinel inclusions were noted in each
Detailed examination showed that apricot
of the 3 horizons. The Middle Terrace (T4A)
coloured stones are actually light pink rubies,
stones show higher (10%) spinel inclusions, fu-
but the orange/apricot colouration is due to
sion crusts and percussion marks in the resorbed
penetration by iron oxide minerals into numer-
and heavily fractured stones.
ous fractures and fissures within each stone.
Medium All 4 horizons show high percentages
Light Apricot Resorption and heavy fractur-
of resorbed and heavily fractured stones; Only
ing dominate stones from Upper Terrace grav-
the Recent Alluvials contain stones with fusion
els (Section18-B) and contain < 10% sapphirine
crusts and spinel inclusions in < 5%.
and spinel inclusions. Section T4A, (Middle
Dark Resorbed and heavily fractured stones are
Terrace) shows > 20% fusion crusting on stones.
predominant in all 4 horizons. Only the Recent
One stone showed pronounced surface resorp-
Alluvials and Section 18-A feature stones with
tion, with intersecting fluid inclusion trails.
percussion marks.
Dark Apricot Less than 10% of stones have
Blue-greenish-yellowish Group (BGY) sapphirine and spinel inclusions in Section 18-
B Upper Terrace, with approximately 10% fu-
Very Pale Resorbed and heavily fractured
sion crusted stones present. Section 18-A Up-
stones are only noted in Section 18-B and the
per Terrace stones show 5% with fusion crust-
Middle Terrace.
ing. Stones from the Recent Alluvials (T2A)
Pale Resorption and heavy fracturing dominate
contain 10% spinel inclusions and 10% fusion
as coupled and single features in stones from
crusting. The Middle Terrace (T4A) contains
both horizons of the Upper Terrace and Recent
30% resorbed, heavily fractured stones showing
Alluvials (T2A), while < 10% fusion crusting,
fusion crusts and nearly 30% resorbed, heavily
percussion marks and spinel inclusions are seen
fractured and fusion crusted stones with sap-
throughout all 4 suites.
phirine inclusions.
Medium High percentages of resorbed and
heavily fractured stones occur in all 4 suites.
Corundum Trace Element Contents
The Middle Terrace shows minor (approxi-
mately 6%) percussion marks. Among the chromophore elements, iron is the
Dark Only resorption and heavy fracturing is dominant trace element and ranges from about
seen as single or combined features in Section 2500 to 13,300 ppm. Titanium ranges from
18-A stones. Section 18-B stones show > 10% about 15 to 1200 ppm, and vanadium is rel-
percussion marks and the Middle Terrace (T4A) atively minor ranging from below detection to
stones contain approximately 12% with fusion nearly 200 ppm. Gallium and chromium are the
crusts and spinel inclusions. only other important trace elements in corun-
Yellowish Resorbed and or heavily fractured dum trace element comparisons, with gallium
stones feature heavily throughout the 4 suites, ranging from below detection to nearly 300
however small percentages (< 5%) of spinel in- ppm. The Cr/Ga ratios of the corundums fall
clusions, fusion crusts and percussion marks into 3 main groups of element ratios and are
are present in the Upper Terrace gravel hori- summarised below.
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110
Colour Fe(ppm) Ti(ppm) Cr(ppm) Ga(ppm) V(ppm) Ca(ppm) Cr/Ga
Colourless 3027-3045±4 15.16±2 BD-6±1 19-20±1 BD 0-49±3i i
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GEMSTONE CHARACTERISTICS 111
Grns Ns Ni Na ρ s(106 ) ρ i(106 ) U(ppm) Age(±1σ)
Latest Cretaceous (1 grain)
1 18 15 100 0.2860 0.2384 10.0 66.5±23.2
Eocene group 1 (av.) Yellow to Orange
8 138 142 100 2.187 2.260 37-138 (Av. 93) 53.7±6.9
Eocene group 2 (av.) Yellow
3 130 146 83 3.013 3.352 8-260 (Av. 140) 48.5±10.0
Eocene group 3 (av.) Red
3 219 275 93 3.769 4.742 148-233 (Av. 200) 43.7±4.1
Oligocene group (av.) Orange to Red
2 266 349 100 3.591 5.554 105-363 (Av. 234) 35.6±3.6
Pliocene group (av.) Red
2 34 443 100 0.540 7.039 252-345 (Av. 298) 4.2±0.7
Table 4. Zircon fission-track results, Gummi Flats. ρD = 1.257–1.284 × 106 cm−2
ND = 1966. Ages calculated using a zeta of 87.7 ± 0.8 for U3 glass.
Analyst P.F. Green.
Grns Ns Ni Na ρ s(106 ) ρ i(106 ) U(ppm) Age(±1σ)
Eocene group (av.)
7 207 179 100 3.290 2.842 101-237 (Av. 153) 49.7±5.3
Pooled age 50.2±2.2
Oligocene group (av.)
6 177 207 100 2.805 3.477 57-417 (Av. 187) 36.8±4.2
Pooled age 35.1±1.5
Early Miocene group (av.)
2 136 243 200 1.743 2.958 48-317 (Av. 108) 23.5±2.7
Pooled age 24.3±1.8
Late Miocene (?)
1 59 277 300 0.313 1.467 79 9.2±1.3
Pliocene Group
2 27 332 350 0.223 2.781 46-289 (Av. 168) 3.5±0.7
Pooled age 3.5±0.5
Table 5. Zircon fission-track results, East Tomalla suite. ρD = 9.906 × 105 cm−2
ND = 1468. Ages calculated using a zeta of 87.7 ± 0.8 for U3 glass.
Analyst P.F. Green.
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112 ROBERTS et al.
Low Cr/Ga Group (< 1) Group 2. (Oligocene) 6 grains (av. U 187 ppm)
Colourless, blue-green, yellow-blue and and central age of 36.8 ± 4.2 Ma.
dark-blue. These characteristically have low Cr Group 3. (Early Miocene) 2 grains (av. U 108
(up to 6 ppm) and high Ga (19 to 299 ppm) giv- ppm) and central age of 23.5 ± 2.7 Ma.
ing very low Cr/Ga ratios (< 0.02–0.34). Group 4. (Late Miocene) 1 grain (U 79 ppm)
and central age of 9.2 ±1.3 Ma.
Mid Cr/Ga Group (6–20)
Group 5. (Pliocene) 2 grains (av. U 168 ppm)
Lavender, grey lavender, violet, purple and
and central age of 3.5 ± 0.7 Ma.
browny pink. These have greater Cr contents
(165 to 501 ppm) and relatively low Ga (22 to
49 ppm), giving Cr/Ga ratios of 6.13–19.20. DISCUSSION
High Cr/Ga Group ( > 20)
Pink, purple pink and red. These contain
Depositional Relationships, Terraces
the highest Cr contents (688–2253 ppm) and rel- and Corundums
atively low Ga (15–52 ppm), giving Cr/Ga ra- Deposits from the three terraces, which yielded
tios of 27–138. the corundum suites, show both differences and
similarities. The lower gravel horizon of the Up-
Zircon Fission-Track Results per Terrace, Section 18-B, lacks obvious allu-
vial characteristics. The horizon is very poorly
Gummi Flats sorted in size and shape of its lithic fragments,
and has a heavy clay matrix; it displays some
Fission-track results have delineated 6 dis- characteristics of a mass debris flow (Cas and
tinctive zircon groups based on uranium con- Wright, 1987). The two upper terrace gravel
tents and age results. horizons occur intermittently over the Gummi
Group 1. (Latest Cretaceous) Yellow colour. 1 Flats area. The upper gravel (Section 18-A)
grain (U 10.0 ppm) and age of 66.5 ± 23.2 Ma. has a different colour and shows slight fining
Group 2. (Early Eocene) Yellow and orange upwards. It contains more sub-rounded lithic
colours, 8 grains (av. U 93 ppm) and central fragments, so could possibly have some alluvialy
age of 53.7 ± 6.9 Ma. derived component, or mark the end of a debris
Group 3. (Mid Eocene) Yellow colour, 3 grains flow.
(av. U 140 ppm) and central age of 48.5 ± The Middle Terrace (Section T4A) dis-
10.0 Ma. plays a clearer fining upwards, compared to
Group 4. (Late Eocene) Red colour, 3 grains Section18-B. The Middle Terrace has a slightly
(av. U 200 ppm) and central age of 43.7 ± larger percentage of rounded and sub-rounded
4.1 Ma. stones, but sub-angular and sub-rounded lithic
Group 5. (Oligocene) Orange and red colours, 2 fragments still dominate. Overall it is poorly
grains (av. U 234 ppm) and central age of 35.6 sorted.
± 3.6 Ma. The Recent Alluvial terrace (Section T2A)
Group 6. (Pliocene) Red colours, 2 grains (av. shows stronger alluvial characteristics than the
U 298 ppm) and central age of 4.2 ± 0.7 Ma. Middle and Upper terraces. Upward fining se-
quences are present, lithic fragment sizes are
East Tomalla
smaller and there is a larger percentage of
Fission-track dating delineated five separate rounded and sub-rounded lithic fragments. The
zircon groups. The colours and uranium con- Recent Alluvial gravels are intermittently over-
tents do not vary greatly within the separate lain by sandy-clays and clays, with sequence
age groups. patterns more typical of alluvially derived de-
Group 1. (Eocene) 7 grains (av. U 187 ppm) posits.
and central age of 49.7 ± 5.3 Ma. The features noted in each corundum suite
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GEMSTONE CHARACTERISTICS 113
help to indicate distances travelled from their likely hosts are the basalts which elsewhere in
sources. Heavy fracturing dominates corun- eastern Australia are known to carry corundum
dums from Recent Alluvials and the lower gravel as xenocrysts (Coenraads 1992), and the corun-
in the Upper Terrace (Section 18-B). Preserva- dums show fusion crusts that indicate reaction
tion of fusion crusts probably indicates a lesser temperatures around 1000◦C (Sutherland and
distance travelled by corundums. The Middle Coenraads 1996). The ruby group in particu-
Terrace has a greater percentage of such crusted lar shows more extensive resorption and indi-
stones. Larger average sizes, poorer gem qual- cates more than one stage of resorption has oc-
ity and more prominent surface inclusions also curred, (up to 80% secondary resorption in some
suggest these stones have undergone less trans- colour suites). This secondary resorption is seen
portation. The corundum traits from the ter- on fractured surfaces, suggesting some fractur-
races suggest the following order of increasing ing took place during igneous explosion events,
transport effects: Middle Terrace, Section 18-A which exposed further surfaces to the corrosive
and Recent Alluvials, Section 18-B. attack.
Overall, sapphirine, and Mg to Fe-rich This magmatic scenario is reinforced by
spinels (pleonaste to hercynite) dominate as in- the fusion crust mineralogy, where spinels
clusions in the corundums. Rubies in all four (pleonaste to hercynite) dominate the main
gravel horizons contain sapphirine inclusions, phases. Sapphirine appears mainly in fusion
indicating a metamorphic origin. The Middle crusts in the ruby suites, but is rarely seen
Terrace rubies contained the largest percentage on blue, green and yellowish corundums. Two
of sapphirine inclusions, over 8%, while Section stones were analysed which showed a dominance
18-B and the Recent Alluvials contain some 2– of pleonaste on one side and hercynite on the
2.5% and Section 18-B under 0.5%. These dif- other side of the same crust, indicating variation
ferences are most likely due to varied transport in crystallization of the spinels during magmatic
processes within the gravels, including distances reactions.
from the sources.
Spinel inclusions are present in all colour Colour-Shade Relationships
groups from the terraces. The Middle Terrace
shows the largest percentages of spinel inclu- The colour-shade histograms clarify relation-
sions, while both the Upper Terrace horizons ships within colour groups from each terrace.
contain similar spinel inclusion percentages and Section 18-B contains less features throughout
the Recent Alluvials the least. These results its colour groups than the other sections. It also
also complicate any linking of the upper hori- exhibits heavily fractured and resorbed stones.
zon gravels (Section 18-A) to the other horizons Fusion crusts along with sapphirine and spinel
as a continuous depositional sequence. It could inclusions exist only in small percentages.
mark a separately derived deposit. When looking at the ruby groups, colour
The Middle Terrace shows higher percent- does not control all the features present within
ages of stones with percussion marks, which these corundums. Section 18-B shows the
may indicate more complex transport processes biggest range of features to occur in the dark
than straightforward alluvial transport. Per- pink colours, whereas in Section 18-A the very
cussion marks need not entirely indicate fluvial pale pinks and dark pinks contain the most
transportation, as they can occur during erup- features, (including an ilmenite inclusion in a
tive processes. dark pink ruby). The Recent Alluvials show
only resorption and heavy fracturing in very
Magmatic Relationships pale pinks, whereas other pink shades show
more varied features. The Middle Terrace shows
The great majority of corundums (50–95%) most variation in corundum features in the pale
show magmatic resorption indicating a hot ig- pink rubys. These ruby histograms clearly show
neous source for their provenance. The most the much higher percentages of fusion crusted
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114 ROBERTS et al.
stones in the Middle Terrace, with pale, medium a blue corundum from section 18-A.
and dark colour groups all containing over 30% The analysis suggest a range of spinel com-
of such stones. positions from pleonaste to hercynite. Only
The blue, greenish and yellowish coloured < 1% of rubies analysed (section T4A) con-
corundums lack sapphirine inclusions, suggest- tained hercynite inclusions, which is more com-
ing their predominant non-metamorphic origin. mon in corundums of magmatic origins (Suther-
Spinel inclusions are found in < 10% amounts land and Coenraads 1996).
throughout these corundums. Only greenish Analyses indicate a clear link between the
corundums from Section T4A (Middle Terrace) mineral inclusions and their host corundum ori-
show > 10% spinel inclusions. Resorption and gins, either as metamorphic (ruby and apricot
heavy fracturing dominate throughout the blue, corundums), or magmatic (some blue, green-
greenish and yellowish colour suites, and none ish and yellowish) types. This correlates well
have > 10% fusion crusts. In comparison to with trace element Cr/Ga ratios in these corun-
the Middle Terrace rubies, which show > 30% dums. For colourless, greens, yellow and blue
fusion crusts in three colour shades the blue, corundums the Cr/Ga ratios are typical of mag-
greenish and yellowish corundums may have matic origin (< 1), while lavender, violet, pur-
undergone greater erosive transport prior to ple, brown pink, pink and red corundums show
their deposition with the rubies. This suggests Cr/Ga ratios typical of metamorphic origin (>
separate origins (i.e. magmatic vs metamor- 1).
phic), eruptive mechanisms and initial trans-
portational processes were involved.
Apricot coloured corundums resemble the Zircon Relationships
rubies, in having > 10% fusion crusted stones
and sapphirine inclusions. As mentioned earlier The zircon fission-track analyses from the
the apricot colour results from iron penetrating Gummi Flats and East Tomalla suites suggest
through fractures and fissures, changing them several eruptive episodes were involved in their
from pale pink to apricot. Thus, these apricot magmatic transport. Correlation between the
two sites show at least three main age groups,
coloured stones were most likely derived from
the same source as the rubies. When compared at around 50 Ma, 35 Ma and 4 Ma, as consis-
to the blue, greenish and yellowish corundums, tent eruptive events. The East Tomalla suite
the rubies and apricot stones show a larger also indicates possible eruption of zircon at
range of features. To elucidate the exact mech- around 23 Ma and 10 Ma. Some earlier erup-
anisms that helped accumulate all these differ- tive episodes for zircon are possible from the
ent coloured stones together will need further Gummi Flats zircon data at around 66 Ma and
detailed investigation. 54 Ma, particularly as these zircons show sub-
stantially lower uranium contents (10–93) than
in the other groups.
Inclusion Relationships
The new zircon age data from northern Bar-
EDAX analysis identified anorthoclase, il- rington areas can be amalgamated with previ-
menorutile and a magnesium, iron aluminosil- ous results for the general Barrington volcanic
icate in addition to previously recorded inclu- plateau (Sutherland and Fanning 2001). The
sions in Barrington Tops corundums. The il- new results not only indicate an extra eruptive
menorutile within a green corundum from the episode at ∼ 50 Ma, but also help to confirm
Recent Alluvials (section T2A), suggests a mag- some previously recorded eruptive episodes at
matic origin which agrees with other blue, both the older (over 65 Ma) and younger (3–
greenish and yellowish corundums in this hori- 5 Ma) ends of the eruptive history. The young
zon. The magnesium, iron aluminosilicate ap- eruptive-age zircons are now known at three
pears in a corundum from the Middle Terrace sites in the Barrington plateau, each one show-
(T4A) and anorthoclase was found included in ing distinctive U contents and colours. This
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GEMSTONE CHARACTERISTICS 115
suggests several geographically separate erup- 9. Although the precise corundum sources re-
tion sites were involved. The complex history of main to be located, the terrace study has nar-
zircon-eruptive episodes would provide multiple rowed down potential source targets, with the
opportunities for associated corundum release Middle Terrace indicating a possible nearby
into the Barrington drainage systems. source.
CONCLUSIONS ACKNOWLEGMENTS
Cluff Resources Pacific N.L. helped by provid-
1. The terrace deposits in the northern Barring- ing research facilities; Tony Baldridge helped
ton area, show some differences in corundum with field work and concentrate preparation.
features within the separate horizons. Gale Webb, Australian Museum assisted with
2. The ruby suite from the Upper Terrace (Sec- gemstone examination. Gary Jeffrey and Scott
tion 18-B), generally lacks fusion crusts, inclu- Stewart, Paradise Palms NSW, took the Aus-
sions and are heavily fractured. This suggests tralian Museum workers to the East Tomalla
greater transport processes for these corun- gemstone lease. Dr Robert Creelman, School of
dums. This contrasts with the deposit in which Science, Food and Horticulture, University of
the corundums occur, as it shows mass deposit Western Sydney made constructive comments
features with no prolonged transportation. on the work, while Curt Stocksiek from the Uni-
3. The Middle Terrace corundums, particularly versity of Western Sydney provided assistance
the ruby suite show the most fusion crusts and with EDAX analysis. Dr Mary Garland, from
inclusions, suggesting a more proximal origin. the University of Toronto, Canada, provided
4. The Recent Alluvial corundums show some PIXE analyses on Barrington corundums. Dr
features that characterise both the Upper and Paul Green, Geotrack International P.L., West
Middle Terrace horizons. This suggests it may Brunswick, Victoria, facilitated zircon fission-
contain some corundums derived from these track analyses.
horizons. These corundums, however, also show
features that suggest sourcing from additional
REFERENCES
areas.
5. As the rubies generally show a difference Cas, R.A.F. and Wright, J.V., 1987. Volcanic
in transport-derived features, it is possible that Successions, Modern and Ancient. Chapman
the other colour groups have undergone sepa- and Hall, London.
rate transportation before amalgamation with Coenraads, R.R., 1992. Sapphires and ru-
the rubies in each terrace. bies associated with volcanic provinces; Aus-
6. Colour Shade histograms and EDAX anal- tralian Gemmologist, 18, 70–80.
yses of corundum inclusions and fusion crusts Galbraith, R.F., 1981. On statistical models for
emphasise the distinct differences between the fission track counts. Mathematical Geology.
ruby and other corundum groups. 13, 471–488.
7. The trace element data further distinguish Gailbraith, R.F., 1988. Graphical display of
the ruby suites from the other corundums, with estimates having differing standard errors.
Cr/Ga ratios indicating metamorphic origins for Technometrics, 30, 271–281.
the ruby group and magmatic origins for most Gailbraith, R.F., 1990. The radial plot: Graph-
other corundums. ical assessment of spread in ages. Nuclear
8. Zircons that accompany the corundums tracks, 17, 207–214.
yield zircon fission-track ages that range be- Gilligan, L.B., Brownlow, J.W. and Cameron,
tween 66 Ma to ∼ 4 Ma, and augment the pre- R.G., 1987. Tamworth-Hastings 1;250 000
viously known multiple eruptive history of the metallogenic map. Sydney; New South Wales
Barrington province. Geological Survey.
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116 ROBERTS et al.
Green, P.F., 1981. A new look at statistics in assemblage from the Tertiary Barrington vol-
fission track dating. Nuclear Tracks 5, 77–86. canic province, New South Wales, Australia.
Green, P.F., 1985. A comparison of zeta calibra- Mineralogical Magazine, 60, 623–638.
tion baselines in zircon, sphene and apatite. Sutherland, F.L. and Fanning, C.M., 2001.
Chemical Geology (Isotope Geology Section), Gem-bearing basaltic volcanism, Barrington,
58, 1–22. New South Wales: Cenozoic evolution, based
Hurford, A.J. and Green, P.F., 1982. A on basalt K-Ar ages and zircon fission track
user’s guide to fission track dating calibra- and U-Pb isotope dating. Australian Journal
tion. Earth and Planetary Science Letters, of Earth Sciences, 48, 221–237.
59, 343–354. Sutherland, F.L., Schwartz, D., Jobbins, E.A.,
Hurford, A.J. and Green, P.F., 1983. The zeta Coenraads, R.R., and Webb, G., 1998. Dis-
age calibration of fission track dating. Isotope tinctive gem corundum suites from discrete
Geoscience, 1, 285–317. basaltic fields: a comparative study of Bar-
Mason, D.R., 1989. Barrington. Intraplate Vol- rington, Australia, and West Pailin, Cambo-
canism in Eastern Australia and New Zealand dia, gemfields. Journal of Gemmology, 26,
(R.W. Johnson, ed.), pp. 123–124. Cam- 65–85.
bridge University Press, Cambridge. Sutherland, Lin and Graham, Ian, 2003. Geol-
O’Reilly, S.Y. and Zhang, M., 1995. Geochem- ogy of Barrington Tops Plateau. Its Rocks,
ical characteristics of lava-field basalts from Minerals and Gemstones, New South Wales,
eastern Australia and inferred sources: con- Australia, 56 pp. The Australian Museum
nections with the subcontinental lithospheric Society, Sydney.
mantle. Contributions to Mineralogy and Webb, G., 1997. Gemmological features of ru-
Petrology, 121, 148–170. bies and sapphires from the Barrington Vol-
Sutherland, F.L. and Coenraads, R.R., 1996. cano, eastern Australia. Australian Gemmol-
An unusual ruby-sapphire-sapphirine-spinel ogist, 19, 417–475.
Authors Affiliations
† Cluff Resources Pacific N.L.,
Unit 1, 30 Leighton Place,
30 Leighton Place, Hornsby, NSW
‡ School of Science, Food and Horticulture,
B.C.R.I. Campus University of Western Sydney
North Parramatta, NSW.
⋆ Geodiversity Research Centre, Australian Museum
6 College St, Sydney, NSW.
Six pages consisting of color figures and an Appendix for this article follow.
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GEMSTONE CHARACTERISTICS 117
Plate 1. Resorbed ruby with pre-
served spinel fusion crust. (scale
is in mm).
Plate 2. Resorbed ruby with sap-
phirine inclusion. (scale is in
mm).
Plate 3. Pale to medium blue
sapphire with several spinel in-
clusions. (scale is in mm).
Figure 1. Locality map, study areas, showing
Gummi Flats and East Tomalla sampling sites
(boxes), general topography, drainage and access
trails and location within New South Wales (inset).
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118 ROBERTS et al.
Figure 6. Colour-Shade histograms of Ruby, Blue Group corundums.
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GEMSTONE CHARACTERISTICS 119
Figure 6 (continued). Colour-Shade histograms of Ruby, Blue Group corundums.
Figure 7. Colour-Shade histograms of Grey-Brown-Black (GBB), Apricot, Greenish and
Yellowish Group corundums.
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120 ROBERTS et al.
Figure 7 (continued). Colour-Shade histograms of Grey-Brown-Black (GBB), Apricot,
Greenish and Yellowish Group corundums.
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GEMSTONE CHARACTERISTICS 121
APPENDIX 1
Heavy Mineral Sample Description, East Tomalla
31◦ 49.88´ S 151 ◦ 30.31´ E 1200 m asl
> 2mm size fraction
Magnetic Vol% Description
10 Weathered ferruginous fine-grained olivine basalt
with spinel and clinopyroxene xenocrysts, and
rare feldspar xenocrysts.
Non-magnetic Vol% Description
Spinels 65 Abundant (> 85 Vol % of sample) anhedral to
subhedral, equant to subprismatic, magmatically
corroded, etched and polished spinel xenocrysts
(some with thin basalt rinds) up to 10 mm. Rare
crystal faces present on some grains.
Glassy volcaniclastics 1 Uncommon dark brown to black, finely banded,
scoriaceous, vesicular vitric tuff.
Other rock and mineral fragments 24 Moderately common muscovite aplite, muscovite
granite, fine-stained quartz fragments, gibbsite
and lateritic ironstone.
Uncommon dark brown to black anhedral
prismatic magmatically corroded and polished
clinopyroxene xenocrysts and well rounded milky
quartz grains.
Rare massive monazite.
continued on next page. . .
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122 ROBERTS et al.
< 2mm size fraction
Magnetic Vol% Description
< 0.01 – 10 Well rounded spherical to ovoid fragments of
weathered ferruginous olivine basalt and iron-
stone (> 1 mm) and well rounded, equant, spher-
ical to ovoid highly pitted spinels, some with ad-
hering basaltic crust (< 1 mm).
Non-magnetic Vol% Description
Spinels 50–90 Grey to black, angular to well rounded, equant to
subprismatic, anhedral to subhedral, smooth to
highly pitted, commonly partially resorbed and
magmatically corroded grains with rare crystal
faces.
Lherzolitic detritus ∼1–5 Olivine-common, olivine-green to yellow-green
anhedral, equant to subprismatic, generally
glassy angular grains with pronounced conchoidal
fracture.
Orthopyroxene-uncommon, brown-bronze glassy,
partially to highly resorbed, finely etched and
striated, anhedral to subhedral, short pris-
matic to prismatic, angular to subrounded
grains.Clinopyroxene-uncommon, lime-green to
emerald green (Cr-diopside), partially resorbed,
finely etched and striated, subhedral subpris-
matic, angular to subrounded grains.
Rock and mineral fragments 9–40 Quartz, abundant and two distinct types:
1. Well-rounded spherical to ovoid opaque white
and Fe-stained grains.
2. Angular to sorted, glassy colourless (some Fe-
stained) equant to prismatic grains.
Muscovite aplite - common as fine grained frag-
ments.
Ironstone and gibbsite - moderately common as
well-rounded grains.
Gorceixite-goyazite - uncommon yellow-brown
resinous concentrically zoned rounded grains.
Zircon - uncommon, generally as well rounded
equant, anhedral to subhedral colourless to pink
(rare yellow-brown) grains. Feldspar - rare, par-
tially resorbed glassy colourless angular subpris-
matic grains.
Corundum - extremely rare (6 grains), generally
pale pink to pink-purple (very rare blue-green)
highly resorbed grain fragments.
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Journal & Proceedings of the Royal Society of New South Wales, Vol. 137, p. 123–149, 2004
ISSN 0035-9173/04/0200123–27 $4.00/1
Studies on Aragonite and its Occurrence in Caves,
including New South Wales Caves
jill rowling
Abstract: Aragonite is a minor secondary mineral in many limestone caves throughout the
world and is probably the second-most common cave mineral after calcite. It occurs in the
vadose zone of some caves in New South Wales. Aragonite is unstable in fresh water and
usually reverts to calcite, but it is actively depositing in some NSW caves.
A review of the cave aragonite problem showed that chemical inhibitors to calcite deposition
assist in the precipitation of calcium carbonate as aragonite instead of calcite. Chemical
inhibitors physically block the positions on the calcite crystal lattice which otherwise would
develop into a larger crystal. Often an inhibitor for calcite has no effect on the aragonite
crystal lattice, thus favouring aragonite depositition.
Several factors are associated with the deposition of aragonite instead of calcite speleothems in
NSW caves. They included the presence of ferroan dolomite, calcite-inhibitors (in particular
ions of magnesium, manganese, phosphate, sulfate and heavy metals), and both air movement
and humidity.
Keywords: aragonite, cave minerals, calcite, New South Wales
INTRODUCTION (Figure 1). It has one cleavage plane {010}
(across the “steeples”) while calcite has a per-
Aragonite is a polymorph of calcium carbon- fect cleavage plane {101̄1} producing angles
ate, CaCO3 . It was named after the province of 75◦ and 105◦ . Aragonite twins on {110},
of Aragon, Spain, where it occurs as pseudo- producing pseudo-hexagonal columnar crystals,
hexagonal twins. Calcite is the more common whereas calcite readily twins on the cleavage
polymorph. plane. Compared with calcite, aragonite is
Aragonite belongs to the orthorhombic crys- harder (3.5 to 4 cf. 3), denser (specific grav-
tal system while calcite has been variously ity 2.930 cf. 2.711) and more brittle (Berry
placed in the rhombohedral (Hurlbut 1970), et al. 1983).
hexagonal, trigonal (Berry, Mason & Dietrich Aragonite is often produced in the growth of
1983) or triclinic (Glazer 1987) crystal systems. marine organisms, particularly in shells. When
Another polymorph of CaCO3 in caves is va- the organism dies, proteins in the shell decay
terite, which belongs to the hexagonal crys- exposing the aragonite. In time, aragonite re-
tal system and is less dense than calcite. It verts to calcite in the near surface environment
has been recorded from cave moonmilk, car- in the presence of fresh water. The deposition of
bide dumps and in the shells of living gas- aragonite is also a the product of chemical influ-
tropods.It is not stable in the vadose environ- ence, or high pressure on calcite. It also occurs
ment and commonly reverts to calcite via arag- in secondary deposits in caves (Siegel 1965, Ford
onite. Other polymorphs include the high tem- & Cullingford 1976) and igneous rocks.
perature and pressure Calcite-IV and Calcite- It is probably the second most common cave
V which are not stable in near-surface environ- mineral after calcite Hill & Forti (1997). This
ments (Carlson 1983). reflects the discovery of extensive aragonite de-
Aragonite often forms with a characteris- posits in caves such as Lechuguilla Cave (Carls-
tic acicular habit known as “church steeples” bad Caves National Park, U.S.A.).
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